Abstract Based on structures determined by X-ray crystallography, ab initio MP2 calculations type A mesoionic rings give geometries in good agreement with observed values. study of four ring systems, each exocyclic oxygen, nitrogen or carbon groups, shows that the presence and configuration lone pairs significantly influences geometry configurational preference. Using a localised bond model NBO...

The preparation of one isomer of each of the 16 enantiomeric pairs of the aldohexofuranose pentaacetates is described together with (1)H and (13)C NMR data. Eight of the isomers have been obtained crystalline. Equilibrium values for the anomeric pairs have been determined.

A water-soluble and neutral polysaccharide was extracted from the current pseudobulbs of Oncidium "Gower Ramsey" during the early inflorescence stage (flower stalk less than 4 cm) by hot water, precipitated with ethanol, and purified with an anion exchanger. From the data of monosaccharide composition and linkage and anomeric configuration analyses, the polysaccharide was identified as a linear...

Three hydrolyzable tannins, nobotannins L, M and N, were isolated from the water-soluble portion of the leaf extract of Tibouchina semidecandra, and their trimeric structures were elucidated from spectral and chemical evidence. Nobotanins L and N exist as equilibrium mixtures of four anomers due to the presence of two unacylated anomeric centers.

Gold(III) bromide is a suitable catalyst for the stereoselective cyclization of 2-C-malonyl carbohydrates to the anomeric center under retention of one ester group. Reopening of the lactones with alcohols in the presence of TMSOTf affords allyl, propargyl and benzyl glycosides with high α-selectivity.

Bi(OTf)3 and SiO2-Bi(OTf)3 are found to effectively catalyze the Ferrier rearrangement of tri-O-acetyl glycals with different alcohols providing an effective route to 2,3-unsaturated O-glycosides with good anomeric selectivity and good to excellent yields after short reaction times.

nongjia Forest District, a National Natural Protection Region of China. Most of them were recorded to be used as anti-inflammatory agents in the folk. Kaikoujian, the Chinese name of rhizomes of Tupistra chinensis BAK., is a reputed folk medicine in that district because of its potent to markedly reduce carbuncles and to ameliorate pharyngitis. In the course of our studies on the native folk me...

beta-D-Xylosidases are glycoside hydrolases that catalyze the release of xylose units from short xylooligosaccharides and are engaged in the final breakdown of plant cell-wall hemicellulose. Here we describe the enzyme-substrate crystal structure of an inverting family 43 beta-xylosidase, from Geobacillus stearothermophilus T-6 (XynB3). Each XynB3 monomeric subunit is organized in two domains: ...

With the aim of assessing the role that the thymine base of TSAO-T may play in the interaction of TSAO compounds with HIV-1 reverse transcriptase (RT), we have designed, synthesized, and evaluated for their anti-HIV-1 activity a series of 3-spiro sugar derivatives substituted at the anomeric position with nonaromatic rings or with amine, amide, urea, or thiourea moieties that mimic parts or the...

Variation in the wavelength of irradiation in infrared multiple-photon dissociation (IR-MPD) of lithium-tagged glucose-containing disaccharide ions (1-2-, 1-3-, 1-4-, and 1-6-linked isomers of both anomeric configurations) resulted in marked differences in their mass spectral fragmentation patterns. Two-dimensional plots of the fragment yield versus infrared wavelength for each mass spectral pr...